This invention relates in general to cartridge magazines for firearms, and in particular to magazines for column-feed firearms such as pistols or submachine guns.
Semiautomatic and full-automatic firearms such as pistols and submachine guns typically utilize a column feed arrangement to store a supply of cartridges for feeding to the action of the firearm. The column cartridge feed arrangement usually is embodied in a receptacle or well formed in the firearm and configured to receive a cartridge magazine, and separate magazines which typically store cartridges in a linear column. The cartridges in the magazine may occupy a single column, one above the other, as in the 0.45 Colt automatic pistol, or may alternatively occupy a double-column staggered arrangement which increases the number of cartridges storable in a magazine of given length.
Shooters generally prefer magazines that hold a greater number of cartridges. The casual shooter or plinker wants to be able to shoot a greater number of rounds before he must swap magazines or reload an empty magazine (a tedious task), and the combat shooter has an imperative need to increase the number of rounds he can fire without reloading. The conventional linear cartridge magazine, however, has certain inherent limitations limiting the number of cartridges that can be stored and dependably fed to an automatic firearm. One such limitation is the sheer physical length of a straight or curved linear magazine intended to hold, say, thirty cartridges, particularly in the larger calibers such as 0.45 caliber. Another well-known limitation to simply lengthening existing straight magazines is the dependability of cartridge feeding. The cartridges must be urged toward the open end of the magazine by a spring-loaded follower which is compressed within the magazine; that spring must be strong enough to dependably feed all cartridges including the last one, yet the spring must not be so powerful as to prevent feeding the first few cartridges in a fully-loaded magazine. Furthermore, hand-loading cartridges into a straight magazine of thirty or more rounds capacity is tedious and time-consuming, and the increasing compression of the magazine spring makes it increasingly difficult to load the last few cartridges necessary to provide a fully-loaded magazine.
The prior art drum magazine, which is an alternative to the linear magazine, permits a number of cartridges to be stored in a generally cylindrical or spiral path, thereby overcoming one objection to the straight magazine. Drum magazines, however, are generally designed and constructed for use with a particular firearm which was, in turn, designed specifically to accommodate a drum magazine in place of a linear magazine. One example of such a prior-art drum magazine is found in U.S. Pat. No. 2,131,412 to Ostman. Such drum magazines of the art clearly cannot be used or readily adapted for use with pistols or other firearms designed to receive a linear magazine, since such drum magazines have no provision for feeding cartridges along the existing magazine-receiving receptacle of a pistol. One known attempt to provide a drum magazine for use with pistols resulted in the so-called "snail drum" magazine, having a magazine extension which tangentially joins the drum portion of a pistol. Cartridges are fed around the drum of the magazine and are then passed through the extension, exiting the drum on a path at a tangent to the circular or spiral cartridge storage path within the drum. The tangential construction of the snail drum places the drum's center of gravity off-center relative to a firearm fitted with the snail drum, however, thereby detracting from shooting accuracy. Efforts to overcome the off-center problem by bending or curving the magazine extension below the magazine well will cause problems in cartridge feeding, because the spring within the drum magazine has to force cartridges through the drum and then through a magazine extension including a friction-inducing curvature in the plane of cartridge travel.